bcarpman

Ok, from what I understand, X-dimension is the vertical distance between the centerline of the propshaft and the centerline of the carnkshaft? Correct?

So if this is the case, without knowing how high the engine is in the boat, saying "my X-dim is 18 inches" tells us absolutely nothing. True?? Saying "I have a high X-dim" makes absolutely no sense as well.

For instance, I'm doing some transome repair this fall and may raise the engine and drive 2 inches in the boat. My X-dim won't change, but my prop will be 2 in closer to the surface.

If the above is true and you're really trying to compare how deep the prop is in the water, wouldn't we want to settle on some term that represents the distance from the bottom of the hull to the propshaft?

I bring this up because I keep seeing X-dim brought up in conversations where x-dim does not seem to be relavent.

smiklos@sunprint

iTrader: (1)

X dimension is the distance from the bottom of the boat to the center of the drive input shaft. In the case of a bravo if your centerline was 18" above the bottom your x dimension would be 18. In this example the propshaft would 3"15/16" below the bottom of the boat.
Steve

bcarpman

OK, that makes a little more sense, but it sounds like it still isn't the term that most people seem to think it is (as evidenced by post #2). However, as long as the distance from driveshaft to propshaft stays the same increasing the x-dim raises the drive. But that assumes the same drive is used boat to boat (no shorty lowers, etc.). So saying "my x-dim is 18inches" doesn't tell us anything until we know the drive configuration used?

In a couple of posts I've seen people use the term to directly indicate drive height and I swear in one instance the discussion went on and on assuming a numerically larger x-dim means a deeper prop (it's the opposite)

A term for the distance from the propshaft to the bottom of the boat would be more usefull, since obviously the distance between propshaft and driveshaft does change depending on the drive config.

thanks

badluck

X-dimension (bottom to crank centreline) measurement is used for cutting the transom.
Higher X = higher prop shaft height. The distance between the prop shaft and crank centre line differs between drives.
Like Smiklos stated 18" X on a B1 will give you a prop shaft height of about 4" give or take depending on the transom angle.

Steve Zuckerman

And,
Shorty lower units and/or spacers do not change your X dimension. They DO change your prop depth (- or +). In your case it would be easier to test some shortys and props, than recut your transom. A lower CG does result in better handling, and depending on your engine configuration, you may run out of vertical space beneath your engine hatch.
Regards,
Steve

Falcon

Ok, here goes!X Dimension: The term "X" relates back to right angle triginometry, the hypotenuse of a right angle triangle is sometimes referred to as X in the equations. On a boat it is the distance "on the transom" from the bottom of the boat to crankshaft centerline. On an X dimension chart, you determine where you want the propshaft (or in some cases the anti-cav plate) relative to the bottom, and you input the transom angle relative to the bottom, the chart tells you what the "X" dimension is on the transom of the boat to mount the drill fixture. The right angle of the triangle is the vertical dimension (what propshaft position you want) and the level bottom of the boat. The hypotenuse (X) is the measurement on the angled transom. Wow! I really can use some of that math I learned in high school!

bcarpman

Didn't mean to turn this into a discusion of my project. Was only using it as an example of the confusion I was seeing in posts.

I've already added a 2in shorty and picked up 5mph. Propshaft is still 6.25 inches below the hull. Engine also sits WAYYYY low in the hull. Got about 6-8 inches between the aircleaner and the hatch. In fact the engine sits so low that my tailpipes are almost underwater off plane.

Figure I can probably raise the engine a couple inches and still end up lower than the engine height in most boats this size. Would like to find a used extension box, but that also requires raising the engine.

smiklos@sunprint

iTrader: (1)

It would appear your hole is cut for a 15.5" X dimension and the shorty is making it net out to a 17.5" X dimension. If you go much more than 18.5" you may start to have problems depending on weight prop type etc.
Steve

Hydrolift

X=Location of crank shaft center (CC) from lower edge of boat bottom.

socalstone

Yeah it is confusing. I misused "x" a number of times.
Now I say "prop to pad" or "propshaft to bottom of boat" etc. when talking shorties etc.